The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engines combust an air/fuel (A/F) mixture within cylinders to drive pistons and to provide drive torque. Air is delivered to the cylinders via a throttle and an intake manifold. A fuel injection system supplies fuel from a fuel tank to provide fuel to the cylinders based on a desired A/F mixture. To prevent release of fuel vapor, a vehicle may include an evaporative emissions system which includes a canister that absorbs fuel vapor from the fuel tank, a canister vent valve, and a purge valve. The canister vent valve allows air to flow into the canister. The purge valve supplies a combination of air and vaporized fuel from the canister to the intake system.
A fuel diagnostic system monitors the fuel delivery to the engine. A fuel correction value can be estimated based on a measured air/fuel ratio and a commanded air/fuel ratio. If the estimated fuel correction value is outside of certain predetermined thresholds, a diagnostic trouble code can be recorded. Multiples instances of the estimated correction value being outside of the certain predetermined thresholds can cause a Service Engine Soon light to illuminate. Thus, properly diagnosing the fuel delivery can affect warranty.
In addition, to diagnose the fuel delivery, the purge valve is temporarily controlled such that the air and vaporized fuel is prevented from entering the intake system. Such intrusive interruption to the fueling system can affect fuel economy and/or emissions if the interruptions are frequent and/or are for long periods of time.